US2344578A - Composition for coating concrete - Google Patents

Description

v Patented Mar. 21, 1944 COMPOSITION FOR COATING CONCRETE George W. Whitesidea, Anchorage, Ky.

No Drawing. Application June 1, 1942, Serial No. 445,525

4 Claims. (Cl. 260-18) This invention relates to an improved composition for coating freshly laidcement concrete to protect it against the deleterious loss of moisture, and the product resulting therefrom.

Heretofore, the application of a water-impervious coating or film to the surface of freshly laid concrete has been proposed in such patents as Hayden #l,684,671, Rowan et al. #1,867,421 and Reynolds #1,942,000. The coatings proposed, however, are not completely satisfactory primarily because their costs are relatively high when used in the amounts necessary to produce satisfactory water retention efliclencies.

The principal object of this invention is to pro vide an inexpensive, highly efiicient and eflective coating composition or coating membrane for ing qualities, readily forms a thin, continuous,

highly effective coating or membrane when applied to concrete, and provides a highly efllcient and unusually effective water-repellent and water-impervious film for the concrete.

The coating may be sprayed, brushecbor otherwise applied to the concrete. Since its effectiveness depends, to some extent, on the time of application, it preferably is applied as soon as possible after the concrete is poured and processed to finished form. When the concrete is quite wet, it is desirable to delay the application until the superficial water has subsided. Where, as in building constructions, the concrete is encloseby forms, the coating may be applied to the forms before the concrete is poured and to the concrete immediately after the forms have been removed. The coating is effective immediately upon application and continues, as long as it adheres firmly to the concrete, to perform its protective functions efiiciently and effectively. Its adhesive properties are such that it will remain intact long after the concrete has become permanently set unless removed or destroyed by means other than the elements.

The water-insoluble, metallic, fatty-acid soaps are preferably, but not necessarily, taken from the aquaphobic group. Among the soaps satisfactory for use are zinc stearate, aluminum stearate, and any of the palmitates or oleates. A soap made from a technical grade of a fatty acid has been found highly satisfactory for use although it usually contains appreciable quantities of other soaps.

The non-volatile hydrocarbon base or carrier may be either of a bituminous or resinous charstantially colorless.

acter. Where a bituminous base is used, the resulting composition is dark in color. Most resinous bases, on the other hand, produce a final composition which is substantially clear and sub- The clear type is recommended for use on concrete structures such as dams and the like, where appearance is of some importance. It is also recommended for use in concrete roads constructed in warm climates where temperature variations are extreme and where, as a consequence, the dark type is less desirable because of its heat-absorptive properties. The dark type is highly recommended for use where temperature variations are less extreme and also where a highly effective protective coating is desired at minimum cost regardless of pitch and coal-tar pitch, and of the above resins,

cumar, indene and terpene are preferred because, having a low saponiflcation number, they do not react with the constituents of the concrete.

The volatile solvent to be used will be any of the well-known materials capable of dissolving the hydrocarbon and resinous bases mentioned. For example, volatile hydrocarbon petroleum solvents, such as mineral spirits, or, coal-tar solvents, such as toluene, may be used. 1 In the preparation of an exemplary composition made according to my invention, a soap such as aluminum stearate is ground in a ball mill to the particle size which has been found to be best adapted for its mechanical mixture and/or suspension with the base and solvent and the least likely to form a gel at atmospheric temperature except after an infinitely'long'period of time. A grinding mixture composed of 25% aluminum stearate and mineral spirits has been found entirely satisfactory. The resin in a suitable solvent and the ground aluminum stearate are mixed in a suitable mixer, such as the countercurrent pump type, and sufficient solvent added to secure the final desired solvent content.

In the grinding operation and in the subsequent mixing of the solvent, the soap, and the base, it is important that predetermined conditions, particularly as to temperature, be maintained so that there is no tendency for the soap to gel. Such conditions must also be maintained prior to the actual application of the composition. A composition in which the soap is gelled does vnot form a base and an overlying layer of soap when applied to concrete and will not perform as eflicientperatures, the greater portion thereof will remain, I I believe, as a mechanical mixture or suspension and upon application to the concrete will form at the top of the film in overlying layers as hereinafter described. If the temperature of the soap is permitted to exceed these temperatures, gel formation proceeds to a degree dependent upon the time of exposure to the elevated temperature and the temperature itself, the increase in viscosity, by reason of the gel formation, being a direct function of the time and temperature.

.This is established by the following table which gives in column 1 the temperatures at which the viscosities of the various compositions mentioned in the other columns, were measured by the Engler method; in column 2, the viscosities of a composition made in accordance with my invention and containing aluminum stearate incorporated mechanically; in column 3, the viscosities of a similar composition after it had been heated to 194 F'. for one hour to insure the solution and gelation of the aluminum stearate; and in column 4, the viscosities of the same composition after it had been heated to 194 F. for one hour and then allowed to stand for 24 hours.

' It will be noted that in the temperature range between 122 F. and 140 F., the viscosity of my composition (column 2) increases with the temperature. Within a temperature range of 59 F. up beyond 104 F. but not above 122 F., the viscosity curve of my composition can be reversed. Above that range, the aluminum stearate begins to gel and the viscosity curve assumes a different path for each different degree of gelation. Where the compositions are first heated to 194 F. (columns 3 and 4) the formation of gel to avmarked degree is immediately apparent. In these latter cases, the viscosities, at the higher temperatures, decrease because of the increased fluidity of the gel.

- The increased moisture-retention efilciency a soap, such as aluminum stearate, in a basesolvent solution is indicated by the following table wherein column 1 lists the days on which observations were made; column 2 notes the moisture lost from a cement pat covered with a single coating of my composition, thesoap ingredient comprising ground, mechanically-dispersed aluminum stearate; column 3 notes the higher moisture loss under identical conditions except for the omission of the soap ingredient from the composition; and column 4 notes the gain in efllciency due to the addition of the soap, the efficiency gain being calculated on the assumption that each figure in column 3, for the soapless composition, repre- From the above it will be noted that an increased efiiciency as high as 60% is secured during the early setting of the cement when it is most desirable.

Th importance, of maintaining the aluminum stearate in the form of a mechanical dispersion or suspension (which may be accomplished by grinding it into the base-solvent solution at the non-gelling temperatures previously noted) as distinguished from maintaining it in the form of a gel, is evident from the following table setting forth the comparative results on standard concrete pats. In this table: column 1 lists the days on which the observations were made; column 2, the moisture loss in grams through a single coating containing dispersed aluminum stearate;

column 3, the moisture loss in grams through a single coating containing gelled aluminum stearate; and column 4 the percentage gain in efiiciency of my dispersed composition over the "gelled" composition, the assumed efilciency of the latter being zero.

Moisture loss- 3 a: pats-at 70 F.

Aluminum Alumm 3- y g Mai? a apse Derse e ciency time) by (gelled) of 2 over 3 enn Gram Gram Percent 2 .1 .3 67 4 .3 .7 57 6 .45 .9 50 8 .65 1.1 41 10 .9 1.45 38 14 1.3 2.0 35

which results upon the mechanical dispersion of is clearly understood, it is believed that the nonvolatile hydrocarbon base, when dissolved by the solvent, acts as a carrier for the soap, which remains substantially undissolved. When applied, a good proportion, if not all of the soap, is believed to float to the top of the base or carrier forming a film thereover, consisting of a number of soap layers.- evaporation of the solvent leaving the concrete protected first by the base or carrier, and second by the overlying and, possibly, dispersed particles of soap. The base, unquestionably, acts as a water-proofing or water-retaining agent but not necessarily as a highly efllcient, one. The soap is believed to act as a more efflcient water-proofing or water-retaining and water-repellent agency. As a result, it is believed that the base restricts the passage of water from the concrete to the overlying soap layers, while the soap layers more eflectively restrict the passage to atmosphere of such water as may pass through the base.

To illustrate suitable compositions made in accordance with this invention, the following examples, wherein the proportions are by weight, are given:

V. M.P. naphtha (light petroleum naphtha) 82.6

Aluminum stearate 3.3

Example -Resinous base and terpene Terpene (piccolyte) resin "a 35 Cumar (hydrogenated): 5 V. M. P. naphtha (light petroleum naphtha)- 32.6 Mineral spirits 10.4 Aluminum stearate 3.3

It will be readily appreciated that the relative amounts of base and solvent will depend upon the consistency desired in the composition. Ordinarily, equal parts of both will give excellent re- The base solidifies upon the.

- in the form of a relatively thin film over freshly sults. The soap content of the composition, howproportion to the increased cost. Preferably,

more than 1% of soap should be used since approximately that amount is believedto so into a solution when mixed with the other ingredients, despite the manner in which it is mixed.

The efiectiveness of my composition may be 27, 1939, for Method of and composition for coating concrete. The resinous materials-disclosed in this application are claimed herein, while the bituminous materials disclosed are claimed in my co-pending divisional application Serial No. 502,059, filed September 11, 1943.

Having described my invention, I claim:

1. A coating composition for curing freshly placed concrete comprising: a non-volatile, water-repellent, film-forming base of resinous material; a volatile hydrocarbon solvent for the I base; and a mechanically-dispersed, water-insoluble, water-repellent, metallic, fatty-acid soap, the quantity oi soap being sufllcient to form, when the coating is applied and the solvent evaporated, a layer of undissolved soap overlying the base.

2. A coating composition adapted to be spread in the form of a'relatively thin film over freshly placed concrete as a curing membrane comprising: a non-volatile, water-repellent, film-forming base of resinous material; a volatile solvent for the base; and a substantially water-insoluble, water-repellent, metallic fatty-acid soap mechanically mixed with the solvent and base in th form of a mechanical dispersion.

3. A coating composition adapted to be spread in the form of a relatively thin film over freshly placed concrete as a curing membrane, comprising: a non-volatile, water-repellent, film-forming base of resinous material; a volatile solvent for the base; and a substantially water-insoluble, water-repellent, metallic fatty-acid soap mixed with the solvent and base in theform of a me chanical dispersion and in an amount of between 1% and 5%. v

4. A coating composition adapted to be spread placed concrete as a curing membrane, comprising: a non-volatile, water-repellent, film-forming base including a synthetic resin having a low saponification number; a volatile solvent for the base; and a substantially water-insoluble, waterrepellent, metallic fatty-acid soap mixed with the solvent and base in the form of a mechanical dispersion and of a characteristic to form an upper layer' of undissolved soap overlying a layer of the base when the composition is distributed in the form of a relatively thin film.

GEORGE W. ES.